Spark plug porcelain



NOV. 13, 1934.. I M, BREWSTER 1380 182 SPARK PLUG PORCELA I N Filed June9, 1932 ZIECONIUM OXIDE 1171067215".- Q/ufm/l- 4- M gree and it shortlybecomes practically useless as- Patented Nov. 13, 1934 UNITED STATESPATENT OFFICE I 4 Claims.

, In the accompanying drawing, forming a part of this specification, apreferred embodiment of the invention has been illustrated. I

It is customary to use glazed, shiny porcelain insulators in thespark-plugs employed in internal-combustion engines, arcs between theterminals of which ignite the compressed charges of gaseous fuel toexplode the-latter whereby to perform the work of operating the engine.

Experience has demonstrated that the insulating properties orcharacteristics of such porcelain members depend in substantial measureupon the presence and proper preservation of their surface glaze.

If this becomes materially damaged, the efficiency of the spark-plug isreduced in great dea suitable electrical insulating medium.

Under present-day operating conditions, high gas compressions are usedin the engine-cylinders, and these, combined with the associatedelevated ,temperatures in the combustion-chambers, allow the gases toattack and destroy such highly essential and important glaze, this beingparticularly true when tetraethyl-lead is present in the gases for thepurpose of prolonging or retarding the explosions to avoid objectionabledetonation.

The result is that spark-plugs as now made cannot successfully andsatisfactorily perform their intended functions over an adequately longperiod and frequent replacements are required to keep the enginefunctioning in a reasonably satisfactory manner.

So far as I know, no reliable means has been heretofore forthcoming toavoid or to correct this difiiculty and to-escape the expense ofrepeated installations of new plugs.

My invention aims to overcome this obstacle by coating those glazedportions of the spark-plug porcelain 11 exposed to the action of suchheat and gases with a protective medium 12 which maintains the glazeagainst unduly-rapid deterioration.

Such coating material must be one which will not flux under the degreeof heat to which it is subjected in the engine combustion-chamber andwhich will not be detrimentally affected by the constituents of theethyl gasoline, especially the tetraethyl-lead thereof.

Zirconium oxide is a suitable or appropriate material for this purpose,but oxides of other metals of the alkaline or rare earths would likewiseserve the required p pose,v

These metals are of the groups 2, 3, and 4 of the periodic system, andthe members of such (Cl. 123 1s9) groups having oxides of the highestmelting points are the ones most satisfactory for this purpose, such asthe oxides of glucinum, calcium, barium, strontium, magnesium, scandium,titanium, cerium, etc., with aluminum included.

According to the present preferred method of protecting the spark-plug,characterized as a whole 13, after coating at least that portion of itsporcelain element designed and intended to project into thecombustion-chamber and to be exposed to the gases with zirconium oxide,either by brushing it on or by dipping or spraying, the plug is thensubjected for a short time to a temperature of about 2500 Fahrenheit orover.

At such elevated temperature, the glaze becomes slightly soft, thezirconium oxide is attacked by the glaze and fluxes at the surface ofcontact, so that the glaze and coating become in a measure cemented oradhered together, thus assuring the maintenance of the coating orcovering in proper place under ordinary service conditions. During suchheating, the coating becomes more or less vitrified and it may be leftsomewhat rough or it may preferably be polished to give it a smoothsurface.

If aluminum oxide be employed as a coating material, it willprobably notvitrify suificiently to take a suitable polish, but it may be usedwithout undergoing the polishing operation.

Such an external coating or protective layer over the exposed portion ofthe glazed porcelain intended to besubjected in service to the pressure,heat, and chemical action of the hot gases in the combustion-chamber ofthe engine resists or obviates overheating of the underlying shieldedglaze and also prevents chemical reaction between the protected glazeand the chemical components of the gas, with the favorable result thatthe full electrical insulating properties of the glaze are preservedover a much longer period than has heretofore been possible under likeoperating conditions without such a protecting medium.

The invention has been defined by the appended claims, but it will beunderstood that it is not limited and restricted to the precise andexact details hereinbefore set forth and that these may be modifiedwithin substantial limits without departure from the heart and essenceof the invention and without the loss or sacrifice of any of itsmaterial benefits and advantages.

Whereas I have herein indicated the use of certain oxides as suitablematerials to be used for the coating, the invention is not necessarilylimited thereto, as salts may be employed as the equivathe heat,pressure and chemical action of the engine gases without substantialdeterioration, thus preserving the electrical insulating properties ofthe covered glaze of the porcelain.

2. Aglazed poreclainmember adapted for use as an insulating means in aspark-plug of an internal combustion engine having that glazed portionthereof designed to be subjected to contact with .the gases of theengine covered with a zirconiumoxide protectivecoating capable ofwithstanding the heat, pressure and chemical action of the engine gaseswithout substantial deterioration, thus preserving the electricalinsulating properties of the covered glaze of the porcelain.

3. A glazed porcelain member adapted for use as an insulating means in aspark-plug of an internal-combustion engine having that glazed portionthereof designatedto be subjected to contact with the gases of theengine covered with a protective coating bonded with the glaze andcapable of withstanding the heat, pressure and chemical action of theengine gases without substantial deterioration, thus preserving theelectrical insulating properties of the covered glaze of the porcelain.

4. A glazed porcelain member adapted for use as an insulating means in aspark-plug or an internal-combustion engine having that glazed portionthereof designed to be subjected to contact with the gases of the enginecovered with a protective coating containing zirconium capable ofwithstanding the heat, pressure and chemical action of the engine gaseswithout substantial deterioration, thus preserving the electricalinsulating properties of the covered glaze of the porcelain. s

HERBERT M. BREWSTER.

